PRINCIPLES OF VETERINARY SURGERY 99 



mediate environs, spreading out, by multiplication, directly 

 through the tissues. In their local habitat they elaborate 

 toxins which are absorbed by the usual absorbing channels 

 of the tissues, and then diffused throughout the system. 

 But bacteria themselves are capable of entering the circula- 

 tion and of localizing at points of the body quite remote 

 from the seat of initial infection. The exact manner by 

 which they gain entrance into the blood stream is not defi- 

 nitely settled. They may be taken up by the lymph vessels 

 from the lymph spaces of the infected focus ; they may enter 

 the capillaries when the pressure of the inflammatory 

 exudates exceeds the blood pressure ; or they may enter the 

 veins directly by first producing phlebitis and then travers- 

 ing through the three consecutive layers which are more or 

 less dissolved, separated and weakened by the morbid pro- 

 cess ; and finally they may be englobed by leucocytes which 

 carry them into the current by their amoeboid movements. 



h. The formation of alkalies, notably ammonium, occurs 

 in many microbic cultures. The gas either escapes into the 

 surrounding atmosphere or else combines to form salts of 

 ammonia. Like acid fermentation the production of abund- 

 ant alkaHes inhibits the growth of the microbes that produce 

 it. 



Many bacteria are capable of producing the well known 

 odors of hydrogen sulphide and ammonium, while most of 

 them emit odors peculiar to themselves, some of which are 

 pungent and unpleasant while others are aromatic and 

 agreeable. The production of odors is characteristic of 

 most all bacteria. 



i. Nitrifying bacteria. — Many micro-organisms possess 

 the property of reducing nitrogenous compounds into sim- 

 pler combinations. In the cultivated soil they perform the 

 important function of breaking up nitrogen compounds into 

 combinations assimilable by plant life, and of gathering 



